Jim has the enthusiasm, the energy and above all he’s a fighter. For too long we have sat back when we needed to fight.

He added he was "frustrated" that the Labour party north of the border had not used the 10 point win in the Scottish independence referendum to renew itself in time for the general election.

The Labour heavyweight voiced his concerns that if the majority of Scotland decides to vote for the SNP the country could be faced with a "neverendum".

The decision will come as a blow to Ed Miliband who has faced a wave of media criticism after the leader of Scottish Labour Johann Lamont resigned and delivered a harsh critique of the Westminster party's treatment of its northern stronghold.

Two recent opinion polls put the Labour party far behind the SNP and if replicated on polling day could see Labour lose up to 36 seats, which would seriously jeopardise the party's chances of an overall majority.

Alistair Darling became an MP in 1987 and served in the Blair government as secretary of state for Scotland and was later appointed chancellor of the exchequer under Gordon Brown in 2007. The two men had a fractious relationship, with Darling accusing No 10 of "debilitating" attacks.

He staked out a future position as possible leader of the campaign to keep Britain in the EU. He warned that “If you sit back and wait till the other lot have taken so much ground then you’re on the back foot”.

Former Labour spin doctor and political commentator Alistair Campbell tweeted his praise for Darling:

Have known and worked with Alistair Darling for a couple of decades. Great guy, and was a good minister in every job he did. Politics' loss